大棕蝠下丘听神经元频率调谐的方向敏感性

实验在8只大棕蝠(Eptesicusfuscus)上进行.选取了5个声源方位记录部位对侧80°(C-80°)、40°(C-40°)、0°和同侧40°(I-40°)、80°(I-80°).下丘听神经元的频率调谐曲线的形状有三种V型、封闭型和U型.以C-40°的频率调谐曲线为对照,声源方位改变时,多数神经元频率调谐曲线的形状和最佳频率不变.多数神经元在声源方位由记录部位对侧转向同侧时,频率调谐曲线的锐度(以QndB值为指标)由小变大;神经元在I-80°、I-40°的QndB值显著高于C-80°、C-40°、0°的QndB值.在所观察的47个神经元中,5个声源方位的最低阈值的平均值有显著差异,由高到低的分布为MTI-80°＞MTI-40°＞MT0°＞MTc-80°＞MTc-40°.我们推测,声源方位对神经元频率调谐特性影响的机制,可能是抑制性和兴奋性输入的比例不同而相互整合的结果.

DIRECTIONAL SENSITIVITY OF FREQUENCY TUNING CURVES OFINFERIOR COLLICULAR NEURONS IN BIG BROWN BAT, EPTESICUS FUSCUS

Eight big brown bats Eptesicus fuscus were used for this study. Under free field sound stimulation conditions, we studied the sound direction effect on frequency tuning curves of inferior collicular (IC) neurons. Five azimuthal angles were selected in this study: 80° and 40° contralateral relative to the recording site (C-80°, C-40°), 0°, 80° and 40° ipsilateral relative to the recording site(I-80°, I-40°). Among IC neurons studied, there were three kinds of frequency tuning curves: V shaped, enclosed and U shaped. We compared the sharpness of frequency tuning curves, minimum threshold, and best frequencies of 47 IC neurons determined at 5 azimuthal angles. The minimum threshold(MT) and sharpness of frequency tuning increased as the sound directions changed from contralateral to ipsilateral angles. QndB values at I-80° and I-40°were significantly higher than that at C-80°, C-40° and 0°(Repeated measures ANOVA, p<0.001). The average MT from high to low among 5 azimuth angles was as follows: MTI-80°>MTI-40°>MT0°>MTC-80°>MTC-40°. As sound direction changed, most neurons did not change their best frequencies. This study showed that the MT and sharpness of frequency tuning curves increased as the sound direction changed from contralateral to ipsilateral azimuthal angles. It suggests that sound direction effect on frequency tuning may be through the complex interplay between the excitatory and inhibitory input.